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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>全局变量值</title>
    <script>
        var num = 0;
        function add() {
            for (var i = 1; i <= 5; i++) {
                num++;
            }
        }
        function showNum() {
            add();
            document.write(num);
        }
        showNum();
    </script>
</head>

<body>

</body>

</html>